Cyclopolymers of amino acid-based zwitterionic monomers: N,N-diallyl-methionine, -glycine, and -aspartic acid. Synthesis and application as corrosion inhibitors

The methionine-based zwitterionic monomer [(H₂C = CH-CH₂)₂NH⁺CH(CO₂⁻)CH₂CH₂SMe] (I) has been cyclopolymerized to yield polyzwitterion (II), whereas its copolymerization with the glycine-based monomer [(H₂C = CH-CH₂)₂NH⁺CH₂CO₂⁻] (III) and aspartic acid-based monomer [(H₂C = CH-CH₂)₂NH⁺CH(CO₂⁻)CH₂CO₂H] (IV) afforded respective random copolymers (V) and (VI). Polyzwitterions (II), (V), and (VI) have been characterized via water-solubility, viscometry, thermogravimetric analysis (TGA), FTIR, and NMR spectroscopy. The polymers were investigated for their ability to mitigate of carbon-steel corrosion in 15% HCl at 30–60 °C. The polymers outperformed monomer I owing to their larger surface area and increased number of adsorption sites. At 2 ppm, VI yielded an inhibition efficiency (IE) of 85.2% at 30 °C. The corrosion process followed the Langmuir isotherm model with a ΔG_ads of -50.4 kJ mol^{− 1}. At the 5 ppm concentration, the IE% of VI improved from 87.1 to 98.1 at 30 °C in the presence of KI (400 ppm). The addition of KI led to cooperative coadsorption with synergistic parameter values of 4.47 and 3.89 at 30 and 60 °C, respectively. The remarkable inhibition efficacy of low concentrations of the inhibitor paves the way for its application in oil-well stimulation.